It is no crushing insult to Ava DuVernay's "Selma" that experts dispute its accuracy. In today's movie culture, accuracy only matters when the movie is worth arguing about.

Guardians of President Lyndon B. Johnson's memory are upset that he is portrayed as an obstructionist who had to be persuaded by the brutality of Southern police at the Selma-to-Montgomery protest march into pushing what became the 1965 Voting Rights Act.

"In fact, Selma was LBJ's idea," argues Joseph Califano, LBJ's top domestic affairs assistant, in a Washington Post op-ed. LBJ "considered the Voting Rights Act his greatest legislative achievement, he viewed (Martin Luther) King as an essential partner in getting it enacted — and he didn't use the FBI to disparage him."

In the film, Johnson (played by Tom Wilkinson) is portrayed as resisting King (played by David Oyelowo) on a voting rights push because the president wants to launch his War on Poverty. The film also shows, without directly implicating Johnson, some of J. Edgar Hoover's devious efforts to scuttle King and the movement.

Criticism from Califano and other Johnson defenders prompted DuVernay to respond on Twitter. She called the "notion that Selma was LBJ's idea" "jaw dropping and offensive" to the civil rights organizations and individuals who risked life and limb to make the march a success.

In a later tweet she linked to a 2013 article by Louis Menand in The New Yorker as evidence that "LBJ's stall on voting in favor of War on Poverty isn't fantasy made up for a film."

In another tweet she added, "Bottom line is folks should interrogate history. Don't take my word for it or LBJ rep's word for it. Let it come alive for yourself."

Hulton Archive, Getty Images

President Lyndon Johnson shakes hands with the Rev. Martin Luther King Jr. at the signing of the Civil Rights Act of 1964 in Washington. The two would converse later on the importance of voting rights.

President Lyndon Johnson shakes hands with the Rev. Martin Luther King Jr. at the signing of the Civil Rights Act of 1964 in Washington. The two would converse later on the importance of voting rights. (Hulton Archive, Getty Images)

I did. My verdict? I think both sides are right. The film does take some liberties with historical details in the way that every historical movie does. But, like Steven Spielberg's "Lincoln" and other excellent dramatizations, the core of its narrative quite accurately captures the drama, tragedies and triumphs of events that essentially were the final battles of the Civil War.

As Menand's article details, LBJ ordered up the "the g**damnest toughest voting rights act that you can devise." But, as the movie shows, he also asked King to wait as progress stalled. LBJ feared that Southern opposition to civil rights legislation would drain support from the War on Poverty, Medicare, immigration reform and other issues on his ambitious legislative agenda.

What the film leaves out, as Califano notes, is the dialogue easily available on tapes at the LBJ Presidential Library website of Johnson's 1965 telephone conversations with King on King's Jan. 15 birthday.

The Selma march may not have been LBJ's idea, but, in his characteristic fashion, he makes it sound like his own. Even after passage of his landmark Civil Rights Act a year earlier, LBJ told King, "There is not going to be anything as effective, though, Doctor, as all (blacks) voting."

Johnson goes into great detail on the sort of images of Southern police injustice and voting rights abuses that the movement has to put on television so that "the fellow that didn't do anything but drive a tractor will say, 'Well, that's not right, that's not fair' ... and then that will help us on what we're going to shove through (Congress) in the end."

Two years after iconic news footage of police dogs and fire hoses tearing into peaceful civil rights marchers in Birmingham helped pass the 1964 Civil Rights Act, everybody understood the power of television to accelerate political and social changes that had been stalled since the Civil War.

Yet as former NAACP President Ben Jealous said as we happened to meet in the theater lobby afterward, "The troubling thing about the movie is its relevance today."

Indeed, the historical issues in this film — voting rights, police conduct and equal justice, among others — still dominate headlines. That's why this dispute over a movie's historical accuracy matters more than most Oscar-season chatter. We need to know how far we have come in civil rights history to help us figure out where we're going.